1. Field of the Invention
This invention relates to an apparatus for measuring moisture in seed cotton passing through a conventional cotton ginning system. More specifically, the invention relates to a radial electrode designed, in the same configuration as a feed roller and installed as part of a feed roller of a cotton ginning system. Even more specifically, the radial electrode is insulated from the rest of the system thus forming a signal and a ground. The resultant current flow between the electrode and the ground when properly calibrated produces an accurate measure of the moisture content of the cotton passing between the said feed rollers.
2. Description of the Prior Art
It is common knowledge that many factors may affect the resistance of certain materials such as cotton to electric current flow. The factors include (1) moisture content of the material, (2) bulk density of the material, (3) impurities on the cotton, and (4) electrical path length.
The continuous measure of the moisture content in seed cotton passing through a cotton gin has always been a desirable goal in the ginning industry.
The continuous measure of moisture content in seed cotton could thus result in the beneficial effect of being able to effectively control the moisture content of cotton throughout its flow in the gin. Therefore, the moisture measurement should be made early in the ginning system. The first convenient place in modern cotton gins where the measure can be made is at the automatic bulk feed controller, although other locations such as the extractor-feeders are also convenient locations for making cotton moisture measurements.
The principal function of the automatic bulk feed controller is to meter seed cotton into the ginning system at a rate selected by the ginner. Regardless of the ginning rate, which also is the bulk cotton feeding rate, the quantity of cotton between the feed rollers at any instant is constant. Therefore, by using the feed rollers as rotating electrodes, we obtain a site where, so long as cotton is being metered into the ginning system, the bulk density of the cotton is relatively constant.
The feed rollers in the bulk feed control are radial or star-shaped and are usually 3 to 5 inches apart tip-to-tip. To overcome the variations in electrical path length that would naturally occur with different feed-roller spacing or as the roller electrodes rotate, the notion of including both the signal electrodes and ground separated by insulated spacer disks, into one feed roller was conceived so that path length is now constant and is the distance between adjacent electrodes which is fixed by the thickness of the insulated spacer.
Another major problem found in conventional systems is the short circuiting caused by cotton and trash collecting between electrodes and hopper wall. This is overcome in the instant invention by confining the signal electrode portion of the roller-electrode toward the center of the roller and the grounded portion of the roller-electrode to the ends of the roller. This is accomplished by wiring the electrode internally during construction and bringing a lead wire from the signal electrode through a hole or slot in the shaft to an insulated fitting outside the container wall. By this method insulated shaft bearings are not required and a source of faulty signal is eliminated.
It is the unique design of the instant invention for the radial electrode ("signal" electrode) to be constructed in the same configuration as the feed roller and be installed as part of the standard star-shaped steel feed rollers located in the master feed-control hopper. It must make intimate contact with cotton as it enters the seed-cotton processing system. The electrode being designed to have the same configuration as the feed rollers is mounted as a separate insulated section in the center of one of the feed rollers. This electrode is plated with layers of copper, nickel, and chrome, in that order, to prevent oxidation and to minimize the tendency of cotton to cling to it.
The signal electrode is insulated from the shaft and side sections of the feed roller by acrylic plastic mounts to which the electrode is attached by aluminum bolts threaded into vertical and horizontal portions of the mounts; the side sections of the feed roller are attached to the mounts in like manner. The electrode is 7 inches in diameter and 7 inches long; the acrylic plastic insulator between the electrode and the remainder of the feed roller is 0.75 inches wide. An insulated wire passing through the hollow roller electrically connects the electrode to a bronze fitting at the end of the shaft, where a carbon brush assembly connects the electrode system to the moisture-measuring instrument.
A companion counterrotating feed roller provides a bearing surface against which the electrode roller works to maintain a relatively constant pressure on cotton passing between them. The electrical resistance circuit extends from the signal electrode through the cotton mass to the grounded companion roller, and simultaneously to the side sections of the electrode roller that are at ground potential.
A commercial moisture detector used to measure the electrical resistance of seed cotton passing between the two electrodes reported the electrical resistance as a 0- to 10-millivolt output. This was transmitted to a chart recorded graduated as a 0 to 100 division scale and calibrated to correspond to electrical resistance.
Calibration and performance were established during development as follows:
The radial-electrode system was calibrated to measure both seed-cotton and fiber moisture. Twenty-three bales of cotton representing a wide range of moisture contents were used to establish the calibration. This cotton was harvested by spindle pickers and contained foreign matter typically present in normal cotton production. Moisture-content levels were varied by monitoring ambient relative humidity in the field and harvesting at selected periods, and by controlling the amount of water applied to the cotton harvester spindles.
During calibration the processing rate of seed cotton averaged three bales per hour. The feeder electrodes turned at 1 revolution per minute, giving a mean density of 9.6 pounds per cubic foot for seed cotton passing between the electrodes. The height of cotton in the hopper was maintained at about 4 feet by means of a conventional automatic overflow control switch.
Cotton moisture was quantitated in samples collected as cotton passed through the feed rollers and in lint obtained by hand ginning portions of the seed-cotton sample. The moisture range of seed cotton from the 23 bales was 6.7 to 17.2%. The equivalent moisture range for fiber was 5.2 to 9.2%. Moisture levels higher or lower than these were not necessary because a fiber moisture level of 5.2% is too low and 9.2% is too high for proper ginning; at these levels the detector would indicate a need for remedial action.
Precision instruments were used to calibrate the electrical resistance across the instrument input terminals and its millivoltage response. By means of appropriate equations, the actual electrical resistance of the cotton between the electrodes was converted to equivalent moisture contents of seed cotton or lint. Regression analyses of the data were used to determine the average linear relationship of the amount of cotton moisture to electrical resistance. These data are valid only for the electrode system described here, but they show that the rate of change of moisture content with change in electrical resistance is greater for seed cotton than for cotton fibers and can be used to satisfactorily control gin driers.
During a 3-year period more than 800 bales of cotton passed through the radial-electrode feed rollers with no mechanical or electrical problems.
In conjunction with studies on cotton drying and moisture restoration, the system has also been used to automatically select alternate drying routes through experimental driers based on the cotton's need for drying, and to activate the moisture restoration apparatus when the detector indicates a cotton moisture content too low for proper ginning. This was accomplished by installing cam-operated electric switches on the pen motor hub of the recorder.
The drying phase employed two 24-shelf tower driers for which the total exposure period could be varied from 8 to 20 seconds by selecting 4 drying path combinations. Damp cotton at the input feed controller requiring more than one stage of drying was automatically routed to the first drier and then to the finishing drier. Cotton requiring only one stage of drying or less than a full drier automatically bypassed the first drier and was routed through all or part of the second drier.
The route change valve above the first drier routed cotton through 24 shelves of drier No. 1 when the detector measured seed-cotton moisture at 14.5% or more; this corresponds to 90 divisions of the recorder chart scale. Seed cotton containing less than 14.5% moisture passed through the bottom shelf of tower drier No. 1 and was routed through the 1-, 13-, or 24-shelf drying path of drier No. 2.
When the detector measured seed-cotton moisture at 7.5% or less (this corresponds to 10 divisions of the recorder chart scale), humid air was directed through a feeder chute where the air mixed with the seed cotton, enabling fibers to absorb moisture. When seed-cotton moisture was more than 7.5%, the humid air bypassed the chute and was exhausted outside the gin plant. The feeder chute was located between distributor and extractor feeder and required no special routing of cotton.
Misting nozzles were later installed in the conveyor-distributor to add greater amounts of moisture to the low-moisture cottons. These are activated automatically in conjunction with the humid air subsystem. The need for quality control of cotton during ginning prompts the continuation of this work.